Point-of-transaction workstations employing laser-based readers and/or imager-based readers have been used in many venues, such as supermarkets, department stores and other kinds of retail settings, as well as libraries and parcel deliveries and other kinds of public settings, as well as factories, warehouses and other kinds of industrial settings, for many years. Such workstations were often configured either as vertical slot scanners each resting on, or built into, a countertop and having a generally vertically arranged, upright window, or as bi-optical, dual window scanners each resting on, or built into, a countertop and having both a generally horizontal window supported by a generally horizontal platform and a generally vertically arranged, upright window supported by a generally upright tower. Such workstations were often operated to electro-optically read a plurality of symbol targets, such as one-dimensional symbols, particularly Universal Product Code (UPC) bar code symbols, truncated symbols, stacked symbols, and two-dimensional symbols, as well as non-symbol targets, such as driver's licenses, receipts, signatures, etc., the targets being associated with, or borne by, objects or products to be processed by, e.g., purchased at, the workstations.
A user, such as an operator or a customer, slid or swiped a product associated with, or bearing, the target in a moving direction across and past a respective window in a swipe mode, or momentarily presented, and steadily momentarily held, the target associated with, or borne by, the product to an approximate central region of the respective window in a presentation mode. The products could be moved relative to the respective window in various directions, for example, from right-to-left, or left-to-right, and/or in-and-out, or out-and-in, and/or high-to-low, or low-to-high, or any combination of such directions, or could be positioned either in contact with, or held at a working distance away from, either window during such movement or presentation. The choice depended on the type of the workstation, or on the user's preference, or on the layout of the venue, or on the type of the product and target. Return light returning from the target in the laser-based reader and/or in the imager-based reader was detected to generate an electrical signal indicative of the target. The electrical signal was then processed, and, when the target was a symbol, was decoded, and read, thereby identifying the product.
Early all imager-based, bi-optical workstations required about ten to twelve, or at least six, solid-state imagers having multiple, intersecting fields of view extending through the windows in order to provide a full coverage scan volume in front of the windows to enable reliable reading of the target that could be positioned anywhere on all six sides of a three-dimensional product. To bring the cost of the imager-based workstation down to an acceptable level, it was known to reduce the need for the aforementioned six to twelve imagers down to two imagers, or even one imager, by splitting the field of view of at least one of the imagers into a plurality of subfields of view, each additional subfield serving to replace an additional imager. These subfields also intersected each other in order to again provide a full coverage scan volume that extended above the horizontal window and in front of the upright window as close as possible to a countertop, and sufficiently high above the countertop, and as wide as possible across the width of the countertop. The scan volume projected into space away from the windows and grew in size rapidly in order to cover targets on products that were positioned not only on the windows, but also at working distances therefrom.
Each imager included a one- or two-dimensional, solid-state, charge coupled device (CCD) array, or a complementary metal oxide semiconductor (CMOS) array, of image sensors (also known as pixels), and typically had an associated illuminator or illumination assembly to illuminate the target with illumination light over an illumination field. Each imager also had an imaging lens assembly for capturing return illumination light reflected and/or scattered from the target, and for projecting the captured return light onto the sensor array. Each imager preferably operated at a frame rate of multiple frames per second, e.g., sixty frames per second. Each field of view, or each subfield, was preferably individually illuminated, and overlapped, by a respective illumination field and extended through the windows over regions of the product. Each imager included either a global or a rolling shutter to help prevent image blur, especially when the targets passed through the scan volume at high speed, e.g., on the order of 100 inches per second.
Preferably, to reduce power consumption, to prolong operational lifetime, and to reduce bright light annoyance to operators and customers, the illumination light was not emitted at all times, but was emitted in response to detection of return infrared light by an infrared-based proximity system. Such proximity systems were intended to detect infrared light reflected and/or scattered from a product entering the workstation. However, this was often not the case in practice.
The known proximity system included an infrared (IR) emitter operative for emitting IR light along an IR emission axis centrally located within an IR emission field, and an IR sensor for sensing the return IR light along an IR detection axis centrally located within an IR detection field. The known IR emitter and the IR sensor were typically positioned behind the upright window in the workstation such that the IR emission axis and the IR detection axis were generally in mutual parallelism and generally perpendicular to the upright window.
Since a small, dark-colored product will return a small amount of IR light, the known proximity system typically had a high triggering sensitivity, because the small, dark-colored product had to be detected even in the far field. However, a user standing in front of the upright window and wearing white clothing, for example, could falsely trigger the reading, because the known, highly sensitive, proximity system could not distinguish between IR light returning from the product, or from the user's clothing, or from any other item or person that happened to be in the IR emission field. As a result, items or persons outside the workstation, i.e., in the far field, could falsely trigger the reading.
In addition, the IR emission field and the IR detection field of the known proximity system were not well-defined. The intensity of the emitted IR light, for example, was greatest along the IR emission axis, and then decreased in directions radially of the IR emission axis. The peripheral edges of the IR emission field, however, were not sharp. As a result, items or parts of persons inside the workstation, but not in a selected zone, e.g., directly overlying the generally horizontal window, could also falsely trigger the reading.
In addition, the horizontal platforms of some bi-optical workstations were configured with different lengths as measured in a back-to-front direction away from the upright window. The known proximity system was not readily optimizable to work with both long and short platforms. Thus, if the known proximity system was designed to work with a long triggering volume to accommodate a long platform, and if the workstation had a short platform, then items or parts of persons could easily enter the long triggering volume and could falsely trigger the reading.
To counter such false triggering, it was known to reduce the output power of the IR emitter to thereby attempt to read only targets that were close to the upright window. However, this reduced the sensitivity of the proximity system and created problems for detecting products not only in the far field outside the workstations, even for the larger, white-colored products, but also inside the workstations, especially those having long triggering volumes and long platforms.
Accordingly, it would be desirable to reliably trigger electro-optical reading of a target by, for example, illuminating the target only when the target to be read is in a well-defined, selected zone in a point-of-transaction workstation.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.